In many operations, such as off shore oil well drilling, ship movements along coast lines, rivers and inland lakes, accurate positioning of aircraft during periods of low visibility and for accurate mapping and the like, land vehicle location, and many similar activities, it is desirable to have an accurate navigation system which is relatively inexpensve and easily mounted on small vehicles. Prior art navigation systems utilized for these purposes require a transmitter and receiver aboard the vehicle and a series of transponders situated along the desired course. The transponders are miniature transmitter/receivers which are activated by a signal from the transmitter on the vehicle to retransmit a signal which can be utilized to calculate the range of the transponder from the vehicle. Because the transponders are active devices, they require internal power supplies and periodic servicing. In many instances the transponders must be positioned in remote sites with limited access and servicing can be extremely difficult and time consuming.